b-raf ablation in neuronal precursors leads to hypomyelination of the brain. (A–C) Hypomyelination of different regions of the P18 b-raf^Δ/Δneu brain revealed by immunohistochemistry (IHC) using an α-MBP antibody on paraffin sections. Brown staining indicates MBP+ fibers and cells. The sections were counterstained with hematoxylin. (A) Brain cortex. (B) Detail of the cortex. (C) Hippocampus and the dentate gyrus (arrows). (D) MBP expression determined by immunoblotting of brain lysates. The reduced MBP expression in the b-raf^Δ/Δneu lysates correlates with the results obtained in the IHC.